Nanoscale spatial resolution probes for scanning thermal microscopy of solid state materials

Scanning thermal microscopy (SThM) uses micromachined thermal sensors integrated in a force sensing cantilever with a nanoscale tip that can be highly useful for exploration of thermal management of nanoscale semiconductor devices as well as mapping of surface and subsurface properties of related materials. Whereas SThM is capable to image externally generated heat with nanoscale resolution, its ability to map and measure thermal conductivity of materials has been mainly limited to polymers or similar materials possessing low thermal conductivity in the range from 0.1 to 1 W m−1 K−1, with lateral resolution on the order of 1 μm. In this paper, we use linked experimental and theoretical approaches to analyse thermal performance and sensitivity of the micromachined SThM probes in order to expand their applicability to a broader range of nanostructures from polymers to semiconductors and metals. We develop physical models of interlinked thermal and electrical phenomena in these probes and their interaction with the sample on the mesoscopic length scale of few tens of nm and then validate these models using experimental measurements of the real probes, which provided the basis for analysing SThM performance in exploration of nanostructures. Our study then highlights critical features of these probes, namely, the geometrical location of the thermal sensor with respect to the probe apex, thermal conductance of the probe to the support base, heat conduction to the surrounding gas, and the thermal conductivity of tip material adjacent to the apex. It furthermore allows us to propose a novel design of the SThM probe that incorporates a multiwall carbon nanotube or similar high thermal conductivity graphene sheet material with longitudinal dimensions on micrometre length scale positioned near the probe apex that can provide contact areas with the sample on the order of few tens of nm. The new sensor is predicted to provide greatly improved spatial resolution to thermal properties of nanostructures as well as to expand the sensitivity of the SThM probe to materials with heat conductivity values up to 100–1000 W m−1 K−1

How to unravel the chemical structure and component localization of individual drug-loaded polymeric nanoparticles by using tapping AFM-IR

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Absorption Spectroscopy and Imaging from the Visible through Mid-Infrared with 20 nm Resolution

Absorption spectroscopy and mapping from visible through mid-IR wavelengths has been achieved with spatial resolution exceeding the limit imposed by diffraction via the photothermal induced resonance technique. Correlated vibrational (chemical), and electronic properties are obtained simultaneously with topography with a wavelength-independent resolution of ≈20 nm using a single laboratory-scale instrument. This marks the highest resolution reported for PTIR, as determined by comparing height and PTIR images, and its first extension to near-IR and visible wavelengths

Nanometer-Scale Infrared Spectroscopy of Heterogeneous Polymer Nanostructures Fabricated by Tip-Based Nanofabrication

There is a significant need for chemical identification and chemical imaging of nanofabricated structures and devices, especially for multiple materials integrated at the nanometer scale. Here we present nanofabrication, chemical identification, and nanometer-scale chemical imaging of polymer nanostructures with better than 100 nm spatial resolution. Polymer nanostructures of polyethylene, polystyrene, and poly(3-dodecylthiophene-2,5-diyl) were fabricated by tip-based nanofabrication. Nanometer-scale infrared measurements using atomic force microscopy infrared spectroscopy (AFM-IR) obtained quantitative chemical spectra of these nanostructures. We show chemical imaging of intersecting patterns of nanometer-scale polymer lines of different chemical compositions. The results indicate that for closely packed heterogeneous nanostructures, the spatial resolution of AFM-IR is not limited by nanometer-scale thermal diffusion, but is instead limited by the cantilever sensitivity and the signal-to-noise ratio of the AFM-IR system

Relationships between chemical structure, mechanical properties and materials processing in nanopatterned organosilicate fins

The exploitation of nanoscale size effects to create new nanostructured materials necessitates the development of an understanding of relationships between molecular structure, physical properties and material processing at the nanoscale. Numerous metrologies capable of thermal, mechanical, and electrical characterization at the nanoscale have been demonstrated over the past two decades. However, the ability to perform nanoscale molecular/chemical structure characterization has only been recently demonstrated with the advent of atomic-force-microscopy-based infrared spectroscopy (AFM-IR) and related techniques. Therefore, we have combined measurements of chemical structures with AFM-IR and of mechanical properties with contact resonance AFM (CR-AFM) to investigate the fabrication of 20–500 nm wide fin structures in a nanoporous organosilicate material. We show that by combining these two techniques, one can clearly observe variations of chemical structure and mechanical properties that correlate with the fabrication process and the feature size of the organosilicate fins. Specifically, we have observed an inverse correlation between the concentration of terminal organic groups and the stiffness of nanopatterned organosilicate fins. The selective removal of the organic component during etching results in a stiffness increase and reinsertion via chemical silylation results in a stiffness decrease. Examination of this effect as a function of fin width indicates that the loss of terminal organic groups and stiffness increase occur primarily at the exposed surfaces of the fins over a length scale of 10–20 nm. While the observed structure–property relationships are specific to organosilicates, we believe the combined demonstration of AFM-IR with CR-AFM should pave the way for a similar nanoscale characterization of other materials where the understanding of such relationships is essential